1. Field of the Invention
The invention relates to an arrangement for the contactless determination of an angle of rotation of a rotatable element, in particular a shaft of an internal combustion engine, in which, comprising means for generating a magnetic field rotating with the rotatable element, a magnetic field sensor for detection of magnetic field intensity and an evaluation circuit for determining the angular orientation or position of the rotatable element from the magnetic field sensor output signals.
2. Prior Art
Arrangements of this kind, with which a determination of an angle of rotation can be performed, are known for instance from Published, Non-Examined German Patent Application DE-OS 195 43 562. In these arrangements, a magnet is connected to the rotatable shaft whose angular position is to be ascertained. The magnetic field, which varies with the angle of rotation of the shaft, is measured with the aid of two sensor elements. These sensor elements are either two Hall sensor elements, which are rotatable by an angle of 90.degree. from one another, or two magnetoresistive sensor elements, which are rotated by 45.degree. from one another. The sensor elements are supplied with alternating voltage signals phase offset from one another in a suitable way. The superposition of the output signals of the sensor elements produces a signal course which is representative for the angular position. By suitable linkage of the signals of the two sensor elements, an angle measurement over an angular range of 360.degree. can be obtained. One special application of the known arrangements for contactless determination of an angle of rotation is to detect the angular position of the camshaft of an internal combustion engine. The arrangements described in DE-OS 195 43 562 for contactless determination of an angle of rotation each have two identical sensor elements. This could have disadvantages, because Hall sensors, for instance, have great temperature dependency and great pressure dependency. Magnetoresistive sensor elements, conversely, have better properties with regard to temperature and pressure dependency, being less temperature- and pressure-dependent than Hall sensors, but have the disadvantage that because of the physical effect, only an angular range of 180.degree. can be detected unambiguously. Such an angular range is too small for detecting the position of the camshaft of an internal combustion engine.
Since with the present invention the angle of rotation of the camshaft of an internal combustion engine is intended in particular to be detected, the problems involved in detecting the camshaft angle will first be described below.
To meet the demands for functionality of modern engine controllers, the rpm and the angular position of the crankshaft and camshaft must be detected with high precision at all times. For rpm detection at the crankshaft, a transducer disk with 60-2 angle markings is used, which rotates with the crankshaft and is scanned by a sensor; as the sensor, a sensor that utilizes the inductive, magnetoresistive, or Hall effect is employed.
So that sufficient information about the current operating play of the engine can be obtained, the absolute camshaft position (NW position) must additionally be ascertained. In present engine control systems, the camshaft positions are detected segmentally. A disk that rotates with the camshaft and has one angle marking per cylinder, for instance, is scanned with the aid of a sensor. This sensor outputs an output signal which has one pulse multiple times per camshaft revolution; as a result, current accurate-angle information about the camshaft position is always obtained at the segment boundaries, that is, at the points where pulses occur in the camshaft sensor signal. At the angular positions between segment boundaries, accurate absolute angle information on the camshaft position is unavailable.